It is fairly common practice to inject various chemicals (such as corrosion inhibitors, scale removers, and the like) into the production tubing of an oil well. Usually, such well treatment is carried out by filling the well annulus with chemicals and then injecting the chemical under pressure into the tubing past a control valve located in a side pocket mandrel that is connected in the tubing downhole. It will be recognized that this procedure is not practical for injecting more than one chemical since the chemicals could be intermixed in an undesirable manner. Other systems of upper and lower spaced mandrels have been tried, including a first supply line for injecting one chemical into the tubing at the level of the upper mandrel, and a second supply line for injecting another chemical into the tubing at the level of the lower mandrel. However, these systems have the principal disadvantage that the length of tubing that is connected between the two mandrels is not treated by the chemical that is injected through the upper mandrel because the flowing production fluids carry this chemical upwardly and away from such length of tubing.
The general object of the present invention is to provide a new and improved chemical injection system for treating the entire length of the production tubing located above the lower one of a plurality of injection mandrels with a plurality of chemicals.